Rotation structures, such as bearings, wheels, tires, and so on, are indispensable important parts of existing machine apparatuses.
In the prior art, a rotation structure needs to rotate continuously or discontinuously during a working process. Based on working requirements, a periphery of a rotation structure may need to engage with other components in some cases, for example, in friction transmission. Generally, a periphery of an existing rotation structure is provided with no protection structure, and the bare periphery engages with other components directly or indirectly. Thus, the periphery may be subjected to great radial impact, and the rotation structure may be damaged. Furthermore, the rotation structure is prone to be wetted in working environments, and may contact corrosive gases or liquids directly and be corroded, such that the service life of the rotation structure is adversely affected. Additionally, noise of rotation structures is always a common problem troubling technicians, because most existing rotation structures have the shortcoming of too much noise.